Typically, it takes roughly two years for a roadside-planted tree to become established as a self-sustaining tree. During that time, the tree is especially vulnerable to damage, including mechanical damage, and especially to damage by salt.
In the colder climates, in winter, it is common practice to apply salt to the roads. It is common practice also in winter to snow-plough the roads. As a result, it is common for piles of snow, which often contain high concentrations of salt, to lie heaped at the roadside, sometimes for weeks, and even for months, during the winter.
The roadside, in fact, is a highly disadvantageous location for a new tree. Even if it survives the mechanical damage occasioned by the heaping of the snow, the tree will be surrounded by salt-laden snow for long periods. The salt leaches down through the snow, through the soil, and into the root system of the tree. At the end of winter, when the snow and the ground thaws out, the salt concentration in the soil and roots can be expected to be high: but early spring is just the time when the growth of the tree should be at its most vigorous.
If the salt were to be completely effective in melting the accumulated snow, the situation might be even worse. The melted snow and slush is swept or ploughed onto the verge, with the concentrated salt contained therein. The liquid water then either evaporates or soaks into the ground. Either way, much of the salt leaches into the ground. Of course, some of the salt is washed into the sewers. But a good deal of the salt enters the root-balls of trees planted by the roadside. The salt can remain in the soil for long periods, and builds up over the years as a background level, whereby the rise in salt level over the winter can aggregate to an excessive level.
As a result, roadside trees planted in areas where salt is used to keep the roads clear in winter, are notoriously difficult to establish. In some cases, as many as sixty percent of planted trees fail to become established.
On the other hand, city authorities do desire trees to be established in residential avenues. It is an aim of the invention to provide a means whereby trees may be protected from the effects of heaping salt-laden snow and slush around the not-yet-established trees, which have been recently planted at the side of a road.
It has also been the practice for city authorities to provide mulch on the ground around young trees, to absorb the salt. This practice, though expensive, is effective; however, after the winter, the salt-laden mulch now has to be removed and disposed of. It is an aim of the invention to protect the young trees from salt, but in a manner that does not interfere with the disposal of the salt by normal drainage.